In a conventional method to analyze a sample by using an optical technique, use is made of an analysis unit including a cell in which a reagent is provided (see e.g. Patent Document 1). In this method, a sample is supplied into the cell and reacted with the reagent. The reaction portion of the sample and the reagent is irradiated with light, whereby optical data on the reaction portion such as the amount of light transmitted or reflected are obtained. The sample is analyzed based on these data.
In this method, the sample is often diluted before it is reacted with the reagent. Since the color of the sample becomes lighter due to the dilution, the optical data on the above-described reaction portion are not largely influenced by the color of the sample. Correction processing called “blank correction” is also often performed in this method. Specifically, in the blank correction, a cell provided with a reagent but not provided with a sample is irradiated with light, whereby optical data (blank correction data) on this portion are obtained. By utilizing these data, the optical data on the reaction portion are corrected.
However, the above-described conventional analysis method has the following drawbacks.
In the conventional method, the sample itself is not precisely analyzed before the reaction with the reagent. Thus, even if the sample is not normal (for example, if the color or concentration of the sample is abnormal), the analysis of the sample is still performed, with such abnormalities overlooked. Specifically, in the case where the sample is blood, the blood is yellow when it has a high bilirubin content, red when it is hemolysis and milky white when it is chyle. In the conventional analysis method, even when the sample blood has such an abnormal color, the abnormality is not detected in advance, and the sample blood is analyzed by the reaction with a reagent anyway. Thus, there is a possibility that although the blood itself is abnormal, the abnormality is overlooked and the analysis is regarded as correct. When the blood is diluted before the reaction with the reagent, the above-described color abnormalities are more likely to be overlooked.
The reagent can be provided in a cell of the analysis unit in various manners. For instance, the reagent may be provided in the form of a solid in the cell, so that the surface of the reagent may readily scatter and reflect light. The reagent may include a high content of a substance which has a high absorbance. In these cases, when the cell is irradiated with light to obtain the above-described blank correction data, the light is scattered and reflected by the reagent or easily absorbed by the reagent. As a result, the amount of light which passes through the cell reduces. The blank correction data obtained based on such a small amount of light transmission tends to be incorrect, so that it is difficult to properly correct the optical data on the above-described reaction portion.    Patent Document 1: U.S. Pat. No. 3,526,480